Flow metering

ABSTRACT

A flow meter incorporating thermal loss sensors and an installation adapter to provide known flow conditions upstream of the meter. The installation adapter is in the form of a tubular extension projecting from a flange which in use is sandwiched between a pipeline flange and a flow meter flange. The flanges are configured such that a passageway defined by the adapter extension is located in a predetermined position relative to the flow meter. The flow meter may comprise a sensor array supporting at least three sensors which are not in alignment, one of those sensors being located centrally within the flow meter and the others being distributed at equal distances around the central position. In use, normal readings may be taken from a single one of the sensors, the other sensors being used for initial calibration and subsequent calibration test purposes only. A comparison is made between the relative values of the outputs of the different sensors to identify sensor drift or potentially significant changes in flow conditions.

This application is a 371 of PCT/EPO02/04637 Apr. 26, 2002.

FIELD OF THE INVENTION

The present invention relates to flow metering, and in particular to aflow meter installation adapter, a flow sensor array, and a method foroperating a multi-sensor thermal loss flow meter.

BACKGROUND OF THE INVENTION

Flow meters are well known devices that can be used to measure the rateof flow of a fluid such as a liquid or gas through a pipe. Known flowmeters monitor various conditions such as the rate of loss of heat froma heated sensor or differential pressures to provide an outputrepresentative of flow conditions within the body of a flow meter. Eachtype of known flow meter has its advantages and disadvantages but withmany flow meters and in particular thermal loss flow meters it isdifficult to pre-calibrate a meter without a precise knowledge of theoperational environment in which that meter is to be fitted. As aresult, it is often the case that flow meters are delivered to the enduser on the basis that after installation they will be adjusted suchthat the flow meter output does represent a true measure of the flowthrough the meter. Such an approach requires highly skilled techniciansto install meters and it would clearly be highly desirable to rely uponfactory-calibration to a much greater extent than is possible atpresent.

One problem encountered when installing flow meters is that such metersare generally inserted between flanges of a pipeline. Thus the flowmeter will define an inlet of factory-determined dimensions which in useis located downstream of a passageway defined by a pipe of unknowndimensions. Even if for a particular installation the nominal internaldiameter of a pipe upstream of the intended meter location is known,there is almost inevitably a discontinuity as between the meter bodyinlet and the pipe immediately upstream of that inlet which generatesunpredictable effects within the meter body. Such unpredictable effectsmake it impossible reliably to calibrate a flow meter until that flowmeter has been installed in its final place of use.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate theproblem outlined above.

According to the present invention, there is provided a meterinstallation adapter for fitting upstream of a flow meter in afluid-conveying pipeline, the flow meter in use being positioneddownstream of a flange defined by the pipeline, wherein the adaptercomprises a tubular extension having an outside diameter sized to enableits insertion into the pipeline upstream of the pipeline flange, and theadapter has a downstream end configured to engage the flow meter suchthat a passageway defined by the adapter extension is located in apredetermined orientation relative to the flow meter.

Thus, regardless of the internal diameter or condition of the upstreampipeline, the adapter extension provides the flow meter with knownupstream conditions. The internal surface of the pipeline immediatelyupstream of the flow meter is masked by the adapter extension. Inaddition, the adapter extension prevents any gasket used to seal theflow meter to the pipeline flange from protruding into the flowpassageway immediately upstream of the meter.

The tubular extension may itself be mounted on a flange which in use isinserted between a flange of the flow meter and the pipeline flange. Afactory-defined seal may be provided between the flow meter and theadapter flange, obviating the need to provide a gasket of unpredictableconfiguration between the installation adapter and the flow meter.

A meter installation adapter as defined above does make it possible topredetermine conditions immediately upstream of a flow meter and therebyto improve the accuracy of factory calibration of a flow meter. Theconditions in which the flow meter is used can however change in anunpredictable manner as a result of other factors, for exampleinstability in the flow resulting from upstream bends anddiscontinuities in the pipeline, particularly when flow rates vary to asubstantial extent. For example, if a thermal loss flow meter providedwith a single thermal loss sensor is calibrated on the basis that afully developed flow is expected in the vicinity of the sensor, and yetconditions change such that the fully developed flow is disrupted, therelationship between the sensor output and the flow may be radicallyaltered, rendering the meter output inaccurate. If a single sensor ispositioned at three quarters of the radius of the pipeline away from thepipeline axis in a position which can be represented at 12 o'clock, thesame sensor located at the same distance from the pipeline axis at aposition which could be represented as for example 3 o'clock couldproduce a very different output if the flow meter is positioneddownstream of a disturbance creator such as a single bend in one planeor more complex bend combinations. Where a flow meter is positionedother than in a fully developed flow a change in flow rate can in effectcause a rotation in the flow conditions in the vicinity of the flowmeter. A flow meter calibrated in one set of conditions therefore mayprovide inaccurate data if those conditions change.

It is known to manufacture a flow meter in which wires extend across thepassage through which flow is to be monitored, sensors being located atintersections of the wires. Such an arrangement gives a gooddistribution of sensing points within the passageway, enabling the userto generate a flow representing output based on the combination ofoutputs from the different sensors. Such an arrangement is howeverdifficult to install and maintain.

It is also an object of the present invention to obviate or mitigate theproblems outlined above with regard to flow sensing structures.

Thus, according to a second aspect of the present invention, there isprovided a sensor array for positioning in a passageway through whichfluid flow is to monitored, comprising a unitary support extending fromone wall of the passageway and extending at least partially around acentral portion of the passageway, and at least three flow sensorsmounted on the support in a non-linear array. By mounting three or moresensors on an annular or similarly shaped structure sensors capable ofdetecting asymmetry in flow can be provided in a simple and robuststructure. Preferably that structure also supports a sensor locatedcentrally within the passageway.

Thermal loss flow meters have certain advantages and as a result havebeen installed in a wide range of applications. Such flow meters dohowever have the disadvantage that energy is inevitably dissipated giventhat the flow meters operate on the basis that energy is lost into theflow at a rate related to that flow. In systems where multiple sensorsare required to detect asymmetric flow patterns the energy losses fromthe multiple sensors can become significant, particularly in pipelinenetworks where many flow meters are required.

It is an object of the present invention to obviate or mitigate thedisadvantages in terms of energy loss referred to above.

Thus, according to a third aspect of the present invention there isprovided a method for operating a flow meter comprising a plurality ofthermal loss sensors distributed about a passageway through which flowis to be monitored, wherein during normal operation a single sensor isenergized to provide an output representative of thermal loss due to thenow adjacent that sensor, and an output representative of flow rate isderived from the output representative of thermal loss on the basis of apredetermined calibration relationship between flow rate and thermalloss from that single sensor, the calibration relationship beingestablished on the basis of outputs derived from all of the sensors atcalibration, a representation of the relative values of the outputs ofthe sensors at calibration being recorded, and during use the accuracyof the calibration being tested by energizing all of the sensors andcomparing the relative values of the resultant sensor outputs with therecorded relative values, changes in the relative values as betweencalibration and test being indicative of loss of calibration accuracy.

Given that in normal use for most of the time only one sensor isenergised thermal losses are not substantially increased as comparedwith a system incorporating only a single thermal loss sensor. Periodictesting however by energising all of the sensors and comparing theresultant outputs with pre-recorded outputs enables loss of calibrationaccuracy to be detected.

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectioned perspective view of a flow meter body mountedbetween two flanges of a pipeline and downstream of a meter installationadapter in accordance with the present invention;

FIG. 2 is a sectional view through the assembly of FIG. 1;

FIG. 3 is a view similar to that of FIG. 2 but showing a thermal lossflow meter sensor support structure mounted in the body of the flowmeter shown in FIG. 2;

FIG. 4 is a perspective sectional view through the assembly of FIG. 3;

FIG. 5 is a view from below of the sensor support structure shown inFIG. 4;

FIG. 6 is a view from above showing details of the flow meter housingand the orientation in use of the sensor support structure within thathousing;

FIG. 7 is a perspective sectional view through an alternative embodimentof the present invention incorporating an alternative sensor supportstructure;

FIG. 8 is a detailed view of the sensor support structure of FIG. 7;

FIG. 9 is a cross section through the sensor support structure of FIG. 8showing the positioning of sensors within that structure; and

FIG. 10 is a section on the line 10—10 through the structure of FIG. 9;

FIG. 11 is a perspective sectional view through a second alternativeembodiment of the present invention incorporating a star-like sensorsupport structure;

FIG. 12 is a side view of the sensor support structure of FIG. 11;

FIG. 13 is a perspective view of the sensor support structure of FIG.11;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, the illustrated assembly comprises a flowmeter body 1 defining flanges 2 and 3 sandwiched between a flange 4mounted on one end of a pipeline 5 and a flange 6 mounted on one end ofa pipeline 7. In use, a flow meter sensor (not shown) is supported inthe flow meter body 1 so as to be exposed to fluid flowing in thedirection of arrow 8 through the assembly. A meter installation adapter9 extends into the upstream pipe 5 from the body 1. The adapter issealed to the meter flange 2 by an O-ring 10 that seats against a flange11 on the downstream end of the adapter 9. The outside diameter of theadapter 9 is less than the inside diameter of the pipe section 5 suchthat an annular space 12 is defined outside the adapter 9. The insidediameter of the adapter 9 is the same as the inside diameter of themeter housing 1 and the flanges 2 and 11 are dimensioned such that theaxes of the body 1 and adapter 9 are in alignment. Thus there is nosurface discontinuity at the interface between the adapter 9 and thebody 1 represented by line 13.

As best seen in FIG. 2, the flange 2 supports a lip 14 which projectsover the edge of the flange 11 from which the adapter 9 extends. Theflange 2 remote from the lip 14 also defines a recess to receive aprojecting portion 15 extending in the axial direction from the flange11. This ensures that the installer can ensure that the extension 9 iscorrectly aligned with the body 1. In the illustrated case, the axiallength of the extension 9 is greater than the spacing between theflanges 4 and 6. Such an arrangement could only be installed if at thetime of installation the spacing between the flanges 4 and 6 can beincreased to at least the axial length of the adapter 9. Without anymovement of the flanges 4 and 6 however the flow meter body 1 can beslipped out from the gap between the flanges 4 and 6 without having todisplace the adapter 9. Although clearly it is desirable for the adapterextension 9 to be as long as possible, even the use of a very shortadapter extension enhances the predictability of conditions within theflow meter. For example, an extension only a few millimeters long wouldbe sufficient to remove unpredictable conditions immediately adjacentthe interface between the pipeline flange and the flow meter flange. Forexample such a short extension would prevent a sealing gasket protrudingacross the inlet end of the flow meter.

FIGS. 3 and 4 show the assembly of FIGS. 1 and 2 after a flow meter hasbeen mounted on a side of the flow meter body 1 not shown in FIGS. 1 and2. The flow meter comprises a housing 14 extending upwards from a baseplate 15. As best shown in FIGS. 5 and 6, the base plate 15 supports aprojection 16 defining an arcuate inner surface 17 which is acontinuation of the inner surface of the body 1. A ring sensor 18 issupported on a radial rod 19 extending out of the surface 17. The body 1defines a groove 20 which in use receives a sealing ring (not shown),the plate 15 being secured onto the body by four bolts (not shown)extending through the apertures shown in FIGS. 5 and 6.

The ring 18 supports four sensors (not shown) spaced at 90° intervalsaround the ring. The rod 19 also supports a sensor (not shown) adjacentits end. In use, the sensor supported by the rod 19 is located on theaxis of the passageway defined through the body 1 and each of thesensors supported by the ring 18 is located at a distance from thepassageway axis equal to three quarters of the radius of the passageway.

Referring to FIGS. 3 and 4, given that there is no discontinuity betweenthe inner surface of the adapter 9 and the inner surface of the body 1,flow conditions upstream of the sensor ring 18 are determined largely bythe characteristics of the adapter rather than the characteristics ofthe pipe 5 into which the adapter 9 has been inserted. Therefore themeter can be calibrated in the factory on the basis that conditionsupstream of the meter are known. If the adapter 9 was not present, therewould be a discontinuity as between the opening defined by the meterbody. 1 and the inner diameter of the pipe 5. Furthermore, if a gasketwas used to form a seal between the meter body 1 and the pipe flange 4,the gasket might well project radially inwards on at least one side soas to partially obstruct the inlet end of the meter body 1. The use ofthe adapter in accordance with the present invention therefore ensuresthat conditions upstream of the meter are known with certainty as far asthe upstream end of the adapter.

The sensor support structure shown in FIGS. 3 to 6 provides a robuststructure which is easy to mount within the flow meter, does not presentan unduly large obstruction to flow through the meter, and yet makes itpossible to monitor conditions at four positions spaced around the axisand on the axis itself. As a result a very accurate representation offlow conditions within the flow meter can be obtained. The dimensions ofthe sensor support structure are such however that a relatively largeopening is required as shown in FIG. 6 to enable the insertion andremoval of the structure into the flow meter body. An alternativearrangement which does not require such a large opening as illustratedin FIGS. 7 to 10.

Referring to FIG. 7, a support structure 21 is mounted in a flow meterbody 22 sandwiched between flanges 23 and 24 of a pipeline. A meterinstallation adapter 25 is fitted upstream of the body 22. As in thecase of the embodiment of FIGS. 1 to 6, the adapter is accuratelylocated relative to the body 22 by virtue of the co-operation offormations provided on the body and adapter flanges. In particular, FIG.7 shows a portion 26 projecting from the adapter flange as it is engagedin a radial slot in the periphery of the body flange. The supportstructure 21 differs from that shown in FIGS. 3 to 6 however in thatrather than being circular it is only part circular so as to define whatmay be loosely described as a J-shape. Such an arrangement can bemanoeuvred into position through a much smaller opening in the body 22than is required to receive the full ring sensor structure as shown infor example FIG. 5.

FIGS. 8, 9 and 10 illustrate in greater detail the form of the sensorsupport structure 21 of FIG. 7. The structure comprises a radiallyextending hollow rod 27 and a part-annular portion 28 which is alsohollow. A sensor 29 is located in the closed end of the rod 27 and foursensors 30 are supported inside the part-annular portion 28. The sensors30 are received in an inwardly facing slot formed in the part-annularportion 28 and a metal shim 31 is used to close the slot and protect thesensors 30. The overall assembly is lightweight and the sensors are ingood thermal contact through the structure with the surrounding fluidflow. Given the disposition of the total of five sensors, outputs fromthose five sensors can be used to derive an accurate representation offlow conditions around the structure. Conventional techniques can beused to relate heat loss from the sensors 29 and 30 to local flowconditions. Such conventional techniques may be as described in forexample European Patent No. 460044 entitled “Thermal Mass Flow Meter”,proprietor Endress+Hauser Limited.

The arrangement of FIGS. 7 to 10 includes five sensors. A three sensorarray could be supported on a structure which could be threaded througha relatively small aperture and yet would still be able to senseconditions on the meter axis and at points offset by 90° about the axis.One such structure would have a radially inwardly extending position, anarcuate portion extending around 90° of the passageway, and a furtherradially inwards portion extending to the passageway axes, sensors beinglocated on the axis and at each end of the arcuate portion.

With an arrangement such as that shown in FIGS. 7 to 10, if each of thethermal sensors 29 and 30 is continuously energised so as tocontinuously monitor thermal losses to the adjacent flow, the energyconsumed will be five times that associated with a conventional singlesensor thermal flow meter array. Such losses could be significant incertain applications, particularly where many flow measurements must betaken. The present invention makes it possible to minimise such thermallosses by using all five sensors to calibrate the meter and at intervalsto test the accuracy of calibration but relying upon only a singlesensor for routine flow measurement purposes.

For example, when the flow meter is initially calibrated measurementswill be taken from all five sensors for each of a representative set ofcalibration flow rates such that the output of each sensor at aparticular flow rate is determined. It may be that the outputs fromdifferent sensors differ from each other as a result of for example anasymmetry in the flow around the sensor structure. A relationship cannevertheless be derived as between the output of one of the sensors, forexample the sensor 30 closest to the free end of the part-annularportion of the structure, and the total mass flow. The relationshipbetween the output of that sensor and the other sensors can be recordedhowever so that if at some time in the future flow conditions changethat change can be detected by a review of the relative values of theoutputs of all the sensors. For example, if the flow meter is calibratedon the basis of a fully developed flow such that the outputs of all fourof the sensors 30 are identical, the output from any one of those foursensors could be taken to provide the basic measurement value.Periodically the outputs from the four sensors 30 could be compared and,if those outputs were no longer the same this would indicate a need tore-calibrate as either one of the sensors is malfunctioning or flowconditions have changed from those used at the time of calibration froma fully developed flow to a flow in which conditions adjacent differentsensors 30 are no longer the same.

Initial calibration could be conducted in the factory. The accuracy ofthe calibration could then be checked on installation of the meter andits intended site of use, differences between the sensor outputs beingtaken as an indication that the calibration had to be checked.Similarly, after meter installation the accuracy of the calibrationcould be checked at periodic intervals so as to detect longer termdrifts or loss of calibration accuracy as the result of for examplechanges in the flow conditions immediately upstream of the meter. Thisfacility can be achieved at minimal extra cost in terms of energy giventhat except for relatively short test periods only one of the sensors isenergised.

FIG. 11 is a perspective sectional view through a second alternativeembodiment of the present invention. According to this preferredembodiment of the inventive sensor the sensor support has a star-likestructure. Different views of the sensor support structure of FIG. 11are shown in FIG. 12 and FIG. 13. The star configuration provides a‘balanced’ mounting arrangement for each of the flow sensing elements.This arrangement allows a more balanced distribution of the overallelectrical power to the element network with similar performance fromeach sensor element. That means the performance differences between eachindividual sensor element (time response, stray body heat losses, powerrequired to each element) are less than with regard to the nonsymmetrical arrangement of the sensor elements in the before describedcircular design of the sensor support. According to a preferredembodiment the sensor elements 30 are arranged to the sensor support asshown in FIGS. 12 and 13. It is also possible to attach the sensorelements 30 to the sensor support in a different arrangement.

It is a further advantage of the star-like structure of the sensorsupport means that the sensor can be manufactured potentially cheaperand easier. The new design allows a set of modular components to becreated. Therefore it is quite simple to manufacture an extended rangeof star sensor assemblies to accommodate a wide range of pipe linesizes.

1. A flow meter for measuring the flow through a fluid-conveying pipeline whereby a meter installation adapter is provided fitted upstream of the flow meter in a pipeline, the pipeline defining several flanges, the flow meter being positioned in use downstream of one of the pipeline flanges, wherein the adapter comprises a tubular extension having an outside diameter size to enable its insertion into the pipeline upstream of the other of the pipeline flanges, said tubular extension has a downstream end configured to engage the flow meter such that a passageway defined by the tubular extension is located in a predetermined orientation relative to the flow meter, and wherein the inside diameter of the tubular extension is essentially the same as the inside diameter of the flow meter.
 2. The flow meter according to claim 1, wherein the tubular extension is mounted on said adapter flange which in use is inserted between the flow meter flange and the other of the pipeline flanges.
 3. The flow meter according to claim 1, wherein the flow meter and adapter flanges are configured such that the flow meter may be slipped sideways onto said adapter flange in one orientation only and co-operating surfaces on the flow meter and adapter flanges limit the movement of the flow meter flange relative to said adapter flange beyond the point at which the axes of the adapter and flow meter are aligned.
 4. The flow meter according to claim 3, wherein the flow meter and adapter flanges define projections which determine the relative positions of said adapter and the flow meter.
 5. The flow meter according to claim 2, wherein the flow meter flange defines a recess which receives an O-ring to form a seal between said adapter and the flow meter flanges.
 6. The flow meter according to claim 1, wherein a sensor array is provided positioned in a passageway through which the fluid flow is to be monitored, comprising a unitary support extending from one wall of said passageway and extending at least partially in an area having a predetermined distance to a central portion of said passageway, and at least three flow sensors mounted on said unitary support in a non-linear array.
 7. The flow meter according to claim 6, wherein said unitary support extends at least partially around the central portion of said passageway.
 8. The flow meter according to claim 6, wherein said unitary support has a star-like design.
 9. The flow meter according to claim 6, wherein said unitary support extends to a central position within said passageway and includes an at least partially annular portion supporting a series of sensors at substantially equal distances from the central position.
 10. The flow meter according to claim 9, wherein said annular section supports four sensors spaced at equal intervals around the central position.
 11. The flow meter according to claim 6, wherein each of the sensors is a thermal loss sensor. 